<?php
function myfunction($a,$b)
{
    if ($a===$b)
    {
        return 0;
    }
    return ($a>$b)?1:-1;
}
// Array ( [a] => red [c] => blue )
$a1=array("a"=>"red","b"=>"green","c"=>"blue");
$a2=array("d"=>"red","b"=>"green","e"=>"blue");

$result=array_diff_uassoc($a1,$a2,"myfunction");

print_r($result);